1. Field of the Invention
The present invention relates to a method of manufacturing a two-layer roll and a method of manufacturing a cylindrical member, the methods being favorably applicable to manufacture of rolls having high dimensional accuracy, particularly developing rolls, transfer rolls, paper feed rolls, and transport rolls for use in image forming apparatus, such as electrophotographic copiers and printers and toner-jet copiers and printers; particularly, the methods being favorably applicable to manufacture of charge rolls used to establish a uniform electrostatic charge on, for example, photoconductive members of such image forming apparatus and required to have high dimensional accuracy.
2. Description of the Related Art
Charge rolls of image forming apparatus, such as electrophotographic copiers and printers, must not cause contamination of, for example, photoconductive members and must have predetermined conductivity. In order to meet the requirements, conventionally used charge rolls are of polyurethane or silicone rubber. In view of, for example, prevention of contamination of photoconductive members and establishment of electrostatic charge, conventionally proposed charge rolls are configured such that a coating layer, a surface treatment layer, or a covering tube is provided on the surface of an elastic layer (refer to Japanese Patent Application Laid-Open (kokai) Nos. 06-175470, 05-281831, 2002-040760, and 04-214579). Conventionally, in order to maintain a charging property, charge members have been required to have high accuracy in outside diameter. According to general practice, to meet the requirement, after an elastic layer is polished, a coating layer, a surface treatment layer, or a covering tube is provided on the polished surface of the elastic layer as mentioned above.
In recent years, charge rolls have been required to have a more stable charging property, as well as to reduce discharge noise and cost.
On the basis of the concept that requirements of low cost and high charging property are met by a charge roll that has very low hardness in order to provide a sufficient nip width, at some sacrifice of dimensional accuracy, an attempt has been made to impart to a charge roll the structure such that an elastic layer having high conductivity and low hardness is covered with a tubular surface layer.
In this connection, the present inventors focused attention on a transfer member that the assignee of the present inventor had previously developed (refer to Japanese Patent Application Laid-Open (kokai) No. 2002-244457). The transfer member includes a conductive, elastic foamed layer provided on a support member, and a parting layer provided on the conductive, elastic foamed layer. The parting layer is a sleeve member that is previously formed of a conductive resin. However, the disclosed resin tube fails to provide a target low hardness. When low hardness is imparted to the conductive, elastic foamed layer, the layer cannot be covered with the resin tube after the layer is polished. Thus, the conductive, elastic foamed layer must be formed through foaming within the resin tube. However, the process of foaming within the resin tube fails to provide a roll having low hardness.
A two-layer roll has conventionally been formed as follows. An elastic layer and a foamed elastic layer are formed separately. Specifically, the elastic layer is formed by the steps of molding and polishing, whereas the foamed elastic member is formed by the steps of preforming, foaming, and polishing. An adhesive is applied to the outer surface of the foamed elastic member. The thus-prepared foamed elastic layer is covered with the elastic layer, followed by heat treatment.
The above method of manufacturing a two-layer roll requires a molding (or forming) step and a polishing step for each of the elastic layer and the foamed elastic layer, as well as a step of bonding the elastic layer and the foamed elastic layer. Thus, the manufacturing process becomes complicated and involves high cost.
A conventionally proposed apparatus for manufacturing a roller without a parting line includes a cylindrical seamless pipe held within the cavity of a split mold; spring-type pressure-absorbing means provided at one end of the seamless pipe and adapted to absorb cavity pressure that increases with expansion of unvulcanized rubber charged in the seamless pipe, in the course of vulcanization molding of the rubber; and pressure-reducing means provided at the other end of the seamless pipe and adapted to gradually reduce the equilibrium pressure between the cavity pressure and the spring force of the spring-type pressure-absorbing means when the split mold is opened (refer to Japanese Patent Application Laid-Open (kokai) No. 8-66929).
A conventionally proposed method of manufacturing a two-layer roll includes the steps of forming a silicone sponge layer through molding and polishing; placing the silicone sponge layer in a cylindrical mold, which can be split along the axial direction; injecting liquid silicone into the mold to thereby form a surface rubber layer on the silicone sponge layer; and polishing the surface rubber layer, to thereby obtain a two-layer roll (refer to Japanese Patent Publication (kokoku) No. 6-24733).
A conventionally proposed method of manufacturing a charge member employs a crown-shaped core so as to impart a crown shape to an elastic member, thereby yielding a crown-shaped charge member (refer to Japanese Patent Application Laid-Open (kokai) No. 6-242659).
Since a charge roll must have high dimensional accuracy, polishing is generally performed after molding so as to satisfy required dimensional accuracy. However, dimensional accuracy established by means of polishing tends to vary among charge rolls having low hardness. Meanwhile, when polishing is not performed, axial straightness becomes 0.3 mm to 0.5 mm.
A two-layer roll manufactured by the above-mentioned method has problems in that the center of the outer circumferential surface deviates from the axis of rotation, and the axial straightness deteriorates with resultant run-out of the axis.
A cylindrical member used in a foaming mold for forming the foamed elastic layer or in a cylindrical mold for forming the elastic layer is formed by the steps of performing external cylindrical turning on a structural pipe while using the inner circumferential surface of the pipe as a reference; and honing the internal cylindrical surface of the pipe. However, since an axial straightness deviation of about 1 mm is permitted for a structural pipe, even honing cannot improve the straightness. As a result, a cylindrical member having straightness of high degree cannot be obtained. When such a cylindrical member having poor straightness is used to form a mold, a roll manufactured by use of the mold exhibits poor dimensional accuracy.